Brushless welding generators of the homopolar type have been known for a long time. In a known welding generator of this type (German Pat. No. 686,274) the exciting winding is arranged in the stator between two axially adjacent annular poles. Each of the two annular poles has a pole ring. The pole rings are arranged on the winding-free rotor and can be twisted against one another and against a spring which couples them together. The aim of this arrangement is to maintain the generator voltage, on no-load operation, automatically at a desired safe low voltage and, on ignition or burning the arc, at the necessary high voltage. Regulating or control means are not provided for producing a falling current-voltage characteristic for the welding current.
Although welding generators of the homopolar type have been known for a long time, they have not been used widely in practice. However, brushless welding generators which, for example, comprise an exciting machine and a synchronous generator are in use. The alternating current produced by the exciting machine is rectified so that it can be used to excite the synchronous generator. In order to avoid contact with brushes, it is usual to arrange both machines on the same shaft so that rectifiers, which rotate with the rotor of the machine, can be used to rectify the exciting current for the synchronous generator. Experience has shown, however, that such welding generators are susceptible to trouble due to the rotating rectifiers.
Accordingly, an object of the invention is to produce a brushless welding generator which is simpler in construction and less susceptible to trouble than known brushless welding generators comprising an exciting machine and synchronous generator, and which supplies a falling current-voltage characteristic for the welding current.